vox repeat percussion

[hclip]

Okay, so im trying to build this into a pedal and im going by the parts list and one of the transistors is unlabeled.It uses two other transistors  NTE 6401 , and NTE 123A.What would be my best go for the third...
and if anyone has any tips for this pedal i would love to hear them, some of the parts(if i go by the parts list are a little hard to source).this is my second pedal and im kinda new to this.thanks...

[Dan N]

Hi hclip,

I have never seen the schematic. Where did you find it?

Someone once posted some guts photos here. One transistor was a 2N2645 which would equal the NTE123A. The other transistor was a metal can BC. I can't see the number, but would guess it was just a higher gain silicon NPN. The 3rd transistor was a metal can and there was no way to see the markings.

The NTE6401 is a unijunction. Probably the oscillator.

[hclip]

heres the schematic...holpfully if my link works.
anyways...
Q1 is NTE 6401
Q2 is NTE 123A
Q3 is ?
C1 is 100 uf 12V
C2 is 10 uf 15V ... what could i sub for these (c1,c2)
I can find c2 at newark.com but the 100uf 12V seems to be hard to find.

[Dan N]

Thanks for the schematic!!!

Try a 2n3906, or any silicon PNP you have laying around. Don't worry about getting the exact voltages for those caps. 100uf/15 would be fine.

I uploaded the schematic in normal gif form:
http://users.rio.com/senorris/junk/29618561431s.gif

Thanks again!

[Dan N]

I just noticed, the electro caps (C1, C2) are bipolar.

[hclip]

Wouldnt Q3 be NPN?
Maybe a 2N3904?
And the bipolar thing...doesnt +ll+ just mean non-polarized.
Scince the're electrolytic i was thinking of doing a +ll--ll+ for them but from what ive read in the DIY faq each of the capacitors should be double the value that you need for the circuit because of the series capacitance formula:Ctotal= 1 / (1/C1)+(1/C2).
And i dont think there are any 200uf or 20uf caps.

[hclip]

okay, so i found the non-polar caps through NET for C1 = NPR100m16  C2 = NPR10M16 both are 16 volt.
Would a 2N3904 be okay for Q3?
thanks...

[hclip]

Also, Q2 shows that its a PNP transistor, PNP is when the black arrow is going in right?
But the part list shows Q2 = NTE123A, NTE123A is listed as a NPN transistor.Does this matter, or is the schematic wrong or the part?There is a NTE123AP which is PNP but the voltage maxs are a little higher.

[Dan N]

Hi hclip,

I kind of wish someone else would chime in.

The NTE compliment to their 123AP is the NTE159.

Yes, PNP have the arrow pointing inward. Q2 is PNP. I trust the schematic before I trust a parts list.

You can do what you want, but for me. and probably others here, we have our little piles of transistors we like and use them in everything. Low, med, and high hfe. Build with sockets, and try different trannies until we like the sound. Get our effects built and move on to the next.

Good luck!

[nelson]

Never heard of this before.......

Mod ideas anyone?

[JimRayden]

Hmm, by the descriptions at HC, it's not a "tremolo" but a thing that "repeats" your attack. My guess is that it's a sawtooth tremolo or similiar. Can anyone explain how it works? Or sounds?


----------
Jimbo

[R.G.]

The Vox repeat percussion is an old friend of mine. It's a built-in effect on one of my Super Beatles. I don't know whether the built in came before or after the add-on effect.

The repeat percussion is at its heart a tremolo with an odd LFO.

Consider the envelope of a note. It has an initial high peak, and for guitar trails off with an exponential decay. The cleverness in the repeat percussion was realizing that succeeding sections of exponential decay still sound like a high peak and exponential decay, but at a lower volume.

The repeat percussion has an arrangement in Q2/Q3 that can allow the signal through, or lower its volume. Q2 shunts signal to ground in an amount that depends on the voltage on its base. The UJT (Q1) feeds it a repeating spike-and-decay waveform at the repeat frequency. The "repeated attack" comes from the shape of the LFO acting on the natural and longer decay of the note.

This is actually the first time I've seen that particular circuit. The one I'm remembering uses a JFET as the shunt modulator. Maybe that one is just inside the amps and all the plug-ins are bipolar. The plug ins were that - they were a harmonica-shaped box with a phone plug on the back that plugged into your guitar - as long as it wasn't a strat!

[nelson]

How could you add a depth control?



I think I will knock up a PCB layout for this one.

[hclip]

How could you add a depth control?

I think I will knock up a PCB layout for this one.

A depth control would be nice.Im waitting on some parts to put one together....if anyone has any mod ideas for this one let me know.
Ive seen a proto of one with a depth,rate and a two-way switch.Im not sure what the two-way would be for?

[A.S.P.]

no info for ignorants...

[hclip]

Has anyone tried building this yet?
And has anyone made a pcb layout?
I made one on pad per hole board and it doesnt work, though the signal goes through fine, its just unchanged...no effect.Im gonna go through it tonight and see if i did anything wrong, though everything seems okay...the effect is just not happening.
I used a 2N3904 and 2N3906 for Q2,Q3, if i go with a higher gain tranny the signal just gets weaker.
anyway, i'll let you all know how it goes.
-kyle

[nelson]

http://www.ronsound.com/coming.html

This Page Last Updated Sun, 13 Mar 2005 18:27:36 GMT

[hclip]

http://www.ronsound.com/coming.html

This Page Last Updated Sun, 13 Mar 2005 18:27:36 GMT

Ive actually e-mailed that guy a few times about that pedal and some schematics and he never gets back me.

[A.S.P.]

information lost...

[darryl]

Has anyone got this circuit going, I put together and it comes on but no repeat. I saw the other post sounds like the same problem I am having. I keep at it see what I can find.


Thanks
Darryl